The present application relates to improvements to display layouts and specifically to improved color pixel arrangements and means of addressing used in additive electronic projectors, subtractive flat panel displays, and Cathode Ray Tubes (CRT).
Graphic rendering techniques have been developed to improve the image quality of subpixelated flat panels. Benzschawel, et al. in U.S. Pat. No. 5,341,153 teach how to reduce an image of a larger size down to a smaller panel. In so doing, Benzschawel, et al. teach how to improve image quality using a technique now known in the art as “sub-pixel rendering”. More recently Hill, et al. in U.S. Pat. No. 6,188,385 teach how to improve text quality by reducing a virtual image of text, one character at a time, using the very same sub-pixel rendering technique. In a provisional patent application filed by the same inventor, “CONVERSION OF RGB PIXEL FORMAT DATA TO PENTILE MATRIX PIXEL DATA FORMAT” (Ser. No. 60/290,086; Attorney Docket No. CLRV-003P), now U.S. Patent Publication No. 2003/0034992, hereby incorporated by reference, methods were disclosed to generate subpixel rendering filter kernels for improved display formats, including those formats disclosed herein. Prior art projectors, subtractive flat panel displays, and CRTs can not take advantage of such subpixel rendering.
The present state of the art color imaging matrix, for electronic projectors, subtractive color displays and CRT, use a simple orthogonal grid of square pixels aligned in columns and rows as illustrated in prior art FIG. 5. Image shifting to increase the effective resolution of electronic cameras is taught by Parulski et al. in U.S. Pat. No. 4,967,264, by Plummer et al. in U.S. Pat. No. 4,786,964, by Katoh et al. in U.S. Pat. No. 5,561,460, and by Yamada et al. in U.S. Pat. No. 5,754,226. Lower blue resolution for displays is taught by Sprague et al. in U.S. Pat. No. 5,315,418. These panels are a poor match to human vision.
Full color perception is produced in the eye by three-color receptor nerve cell types called cones. The three types are sensitive to different wavelengths of light: long, medium, and short (“red”, “green”, and “blue” respectively). The relative density of the three differs significantly from one another. There are slightly more red receptors than green. There are very few blue receptors compared to red or green.
The human vision system processes the information detected by the eye in several perceptual channels: luminance, chrominance, and motion. Motion is only important for flicker threshold to the imaging system designer. The luminance channel takes the input from only the red and green receptors. It is “color blind”. It processes the information in such a manner that the contrast of edges is enhanced. The chrominance channel does not have edge contrast enhancement. Since the luminance channel uses and enhances every red and green receptor, the resolution of the luminance channel is several times higher than the chrominance channels. The blue receptor contribution to luminance perception is negligible. The luminance channel acts as a resolution band pass filter. Its peak response is at 35 cycles per degree (cycles/°). It limits the response at 0 cycles/° and at 50 cycles/° in the horizontal and vertical axis. This means that the luminance channel can only tell the relative brightness between two areas within the field of view. It cannot tell the absolute brightness. Further, if any detail is finer than 50 cycles/°, it simply blends together. The limit in the diagonal axis is significantly lower.
The chrominance channel is further subdivided into two sub-channels, to allow us to see full color. These channels are quite different from the luminance channel, acting as low pass filters. One can always tell what color an object is, no matter how big it is in our field of view. The red/green chrominance sub-channel resolution limit is at 8 cycles/°, while the yellow/blue chrominance sub-channel resolution limit is at 4 cycles/°. Thus, the error introduced by lowering the blue resolution by one octave will be barely noticeable by the most perceptive viewer, if at all, as experiments at Xerox and NASA, Ames Research Center (R. Martin, J. Gille, J. Larimer, “Detectability of Reduced Blue Pixel Count in Projection Displays”, SID Digest 1993) have demonstrated.
The luminance channel determines image details by analyzing the spatial frequency Fourier transform components. From signal theory, any given signal can be represented as the summation of a series of sine waves of varying amplitude and frequency. The process of teasing out, mathematically, these sine-wave-components of a given signal is called a Fourier Transform. The human vision system responds to these sine-wave-components in the two-dimensional image signal.
Color perception is influenced by a process called “assimilation” or the Von Bezold color blending effect. This is what allows separate color subpixels (or pixels or emitters) of a display to be perceived as the mixed color. This blending effect happens over a given angular distance in the field of view. Because of the relatively scarce blue receptors, this blending happens over a greater angle for blue than for red or green. This distance is approximately 0.25° for blue, while for red or green it is approximately 0.12°. This blending effect is directly related to the chrominance sub-channel resolution limits described above. Below the resolution limit, one sees separate colors, above the resolution limit, one sees the combined color.
An important aspect of electronic displays is resolution. There are three components of resolution in digitized and pixilated displays: bit depth, addressability, and Modulation Transfer Function (MTF). Bit depth refers to the number of displayable brightness or color levels at each pixel location in binary (base 2) power notation. Addressability refers to the number of independent locations that information may be presented and perceived by the human eye. Modulation Transfer Function refers to the number of simultaneously displayable lines and spaces that may be displayed and perceived by the human eye without color error. In display systems that are addressability-limited, the MTF is half of the addressability. However, MTF may be less than half the addressability, given the system design or limitations in the ability of the human eye to perceive the displayed resolution.
Examining the prior art display in FIG. 1, the design assumes that all three colors should have the same resolution. Additionally, the design assumes that the luminance information and the chrominance information should have the same spatial resolution, both in addressability and MTF. The human eye makes no such assumption.
Thus, the prior art arrangement of overlapping the three colors exactly coincidentally, with the same spatial resolution is shown to be a poor match to human vision.